EUBULUS. That may be true. But when Hook states that there are various structures in the brain adapting it for the part which it has to perform in connection with the mental principle, that there is an organ of memory, for example, I find so many facts which are. favourable to this opinion, that I cannot but regard it as more than a mere hypothesis. As to this point, however, Ergates has had greater opportunities than I have had of obtaining information; and I should be well pleased to hear what he has to say on the subject.

ERGATES. If I comply with your wishes, I must make some small demand on your patience, as, although what I have to say may not be much in substance, it cannot be compressed into a very few words.

We may safely assume, as an established fact, that it is only through the instrumentality of the central parts of the nervous system that the mind maintains its communication with the external world. The eye is necessary to sight, and the ear to hearing; and so with the other organs of sense. But the eye does not see, and

the ear does not hear; and if the nerve which forms the communication between any one organ of sense and the brain be divided, the corresponding sense is destroyed. In like manner it is from the brain that all those impulses proceed by which the mind influences the phenomena of the external world. The division of the nerves which extend from the brain to the larynx destroys the voice. The division of the nerves of a limb causes the muscles of the limb to be paralysed, or, in other words, withdraws them from the influence of the will; and the division of the spinal chord destroys at once the sensibility and the power of voluntary motion in all the parts below the part at which the division is made.

If we investigate the condition of the various orders of vertebrate animals, which alone admit of a comparison with our own species, we find, on the one hand, great differences among them with regard to both their physical and mental faculties, and on the other hand a not less marked difference as to the structure of their brain. In all of them the brain has a central

organ, which is a continuation of the spinal chord, and to which anatomists have given the name of medulla oblongata. In connection with this there are other bodies placed in pairs, of a small size and simple structure in the lowest species of fish, becoming gradually larger and more complex as we trace them through the other classes, until they reach their greatest degree of development in man himself. That each of these bodies has its peculiar functions there cannot, I apprehend, be the smallest doubt; and it is, indeed, sufficiently probable that each of them is not a single organ, but a congeries of organs, having distinct and separate uses. Experimental physiology, joined with the observation of the changes produced by disease, has thrown some light on this mysterious subject. There is reason to believe that, whatever it may do besides, one office of the cerebellum is to combine the action of the voluntary muscles for the purpose of locomotion. The corpora quadrigemina are four tubercles, which connect the cerebrum, cerebellum, and medulla oblongata to each other. If one of the

uppermost of these bodies be removed, blindness of the eye of the opposite side is the consequence. If the upper part of the cerebrum be removed, the animal becomes blind, and apparently stupefied, but not so much so but that he may be roused, and that he can then walk with steadiness and precision. The most important part of the whole brain seems to be a particular portion of the central organ or medulla oblongata. While this remains entire, the animal retains its sensibility, breathes, and performs instinctive motions. But if this small mass of the nervous system be injured, there is an end of these several functions, and death immediately ensues. These facts, and some others of the same kind, for a knowledge of which we are indebted to modern physiologists, and more especially to M. Magendie and M. Flourens, are satisfactory as far as they go, and warrant the conclusion that there are various other organs in the brain, designed for other purposes, and that if we cannot point out their locality, it is not because such organs do not exist, but because our means of

research into so intricate a matter are very

limited.

CRITES. Your proposition being granted, and not denying that there may be original differences in the mental principle itself, we perceive to how great an extent the propensi ties and characters of individuals may depend on their physical organization. One person, for instance, may have a nicer perception of colours than another in consequence of the organ by which colours are distinguished being in the one more, and in the other less, developed.

ERGATES. Or the organ may be so imperfect that the perception of colours may be altogether wanting. In fact, examples of such imperfection are not very uncommon. There are persons who can recognise no difference beyond that of mere light and shade, so that when a scarlet cloth is laid out on the green turf they cannot distinguish even these two complementary colours from each other. The great difference which exists in different individuals as to the perception of musical sounds, or 'the power of numerical calculation, is best ex